The invention relates to a multistage automatic countershaft transmission having speed stages which can be changed by means of centrifugal clutches. The transmission of the invention is particularly suitable for motor vehicles.
The automatic countershaft transmission gears of the state of the art have speed stages that can be changed by means of centrifugal clutches. However, these known mechanisms have not proved to be completely satisfactory. For example, the start of the gear change does not depend on the load of the engine; the first phase of the gear change lies within the speed range v.sub.1 to v.sub.2 (v.sub.1 being the speed range at which a forceless contact of friction parts of the clutch takes place; v.sub.2 being the speed, at which the gear change clutch transmits the full torque with slippage via a higher transmission stage, relative to which it is changed); and the second phase of gear change lies within the speed range v.sub.2 to v.sub.3 (v.sub.3 being the speed range wherein a rigid connection of the gear change clutch takes place). These speeds are mutually dependent and therefore, from the point of view of continuity of movement, a wide speed range v.sub.2 to v.sub.3 of the second phase of gear change (which takes place upon a drop of the number of revolutions of the engine from n.sub.2 at the speed v.sub.2 to n.sub.3 at the speed v.sub.3) unnecessarily widens the speed range between v.sub.1 and v.sub.2 of the first phase of gear change. Therefore, the speed range of the vehicle between v.sub.1 to v.sub.3, where the efficiency of transmission of power is reduced due to slippage of the gear change clutch, becomes larger with an unsuitable course of transmitted forces for driving the vehicle in dependence on its speeds. Such prior transmission gears are also not suitable for more than two speed stages.